Synthesis And Properties Of Mononuclear Lanthanide Single-molecule Magnets Constructed From Oxygen Donor Ligands

The molecular-based magnetic material is a molecular-based system with magnetic physical characteristics,and is generally called molecular magnetic material.The discovery of single-molecule magnets?SMMs?is one of significant breakthroughs for molecular magnetic material and researches on them have become very popular recently.The magnetic relaxation behavior of single-molecule magnets mainly depends on the ground state spin and magnetic anisotropy.Lanthanide ions are the preferred ions for the synthesis of single-molecule magnets because of their large intrinsic magnetic moment and magnetic anisotropy.In this thesis,a series of mononuclear lanthanide single-molecule magnets with novel structures and physical?chemical?functions were synthesized by using oxygen donor ligands.Their structures and properties are further studied,and the methods of synthesizing single molecule magnets with high energy barriers and high blocking temperatures have been explored by tuning the coordination environment and other factors.The main contents are as follows:1.The self-assemble of triethylene glycol?H₂TEG?,18-crown-6 and different lanthanide salts results in two complexes[Dy?H₂TEG??NO₃?₃]·[18-crown-6]?1?,[Dy?H₂TEG?Cl₃]·[18-crown-6]?2?.The coordination geometry around Dy^IIIII ion of complex 1can be assigned to tetradecahedron,while the coordination geometry of the complex 2 is a pentagonal bipyramid.Both compounds exhibit two relaxation processes as a field-induced single molecule magnet.The difference of their magnetic relaxation behavior is caused by the dissimilar of their coordination environment.2.Two mononuclear lanthanide complexes,[Dy?PNO?₆?NO₃?]?ClO₄?₂?3?and[Dy?PNO?₆?H₂O?₂]Br₃?4?,were successfully synthesized by using pyridine-N-oxide?PNO?as ligand.X-ray single crystal diffraction analyses show that complex 4 is chiral,while complex3 is a rare kryptoracemate.The optical activity of these compounds is confirmed by circular dichroism?CD?.Although complex 3 crystallizes in the polar space group,the ability to spontaneously polarize is weak,and the ferroelectric hysteresis loop cannot be observed.Magnetic measurements suggest that the two complexes are field-induced single-molecule magnets.3.A series of isomorphous sulfonic mononuclear lanthanide complexes,[Ln?NAS?₂?H₂O?₆]?NAS?·3H₂O[Ln=Dy?5?,Tb?6?,Er?7?,Yb?8?,Dy_0.06Y_0.94?9?],were separated with 2-naphthalenesulfonate?NSA?as an organic ligand.These compounds crystallize in the chiral space group,and the coordination geometry around the central ion can be described as distorted square antiprism.The CD spectra exhibit opposite Cotton effects,demonstrating the optical active of the single crystal.Magnetic measurements indicate that the presence of weak intermolecular dipolar interactions in complex 5,which can be suppressed by magnetic dilution.The complex 6 containing non-Kramers ions shows no ac signal even under an applied magnetic field,and the complexes 5,7,and 8 containing Kramers ions exhibit magnetic relaxation behavior.Although these compounds all crystallize in the polar space group,they do not exhibit electropolarization behavior.